A polyurethane molecule contains a great number of urethane links, ester bonds, ether links and so on. Coating films of polyurethane are excellent in solvent resistance, wearing resistance, scratching resistance, good flexibility and elasticity, etc. Polyurethane resin exhibits strong adhesion to substrate and high peeling strength, but it is relatively expensive. On the other hand, acrylic resins are suitable for various solvents, are excellent in weather-resistance, even under the condition of relatively high temperature and/or UV radiation, acrylic resins do not decompose easily and do not change to yellow-color. Acrylic resins have wide applicability, and low production costs; but they have disadvantages of poor adhesion to substrate when used in certain cases and give unsatisfied laminating strength. Chinese patent publication No. CN100480288C provides an alcohol-soluble acrylic resin, which has fairly good performances when being used in an ink for printing on plastics, but some important functions, especially the adhesion to substrate needs to be further improved. Chinese patent publication No. CN1035772C provides a process for preparation of an acrylic adhesive, in which a laminated film produced by using the adhesive has an initial peeling strength of 2N/2.5 cm (i.e. 1.2N/15 mm). Chinese patent application with publication No. CN1740257A provides an acrylic adhesive, which has a peeling strength of 1.0 N/15 mm when being used as a laminated film; however, a further improved adhesion and laminating strength thereof, especially for laminated films of PET/LDPE and PA/LDPE, are still needed to be improved. Therefore, there is a demand for developing a novel and modified resin, which could combine the advantages of polyurethane resin with that of acrylic resin, and could overcome drawbacks with each other at the same time when being used for preparing ink, laminating adhesive and gloss varnish for woodware.
Recently, more researches focus on modification of acrylic resins, but most of them regarding polyurethane-modified acrylic resins are limited to synthesis of polyurethane-acrylic resin emulsions. The preparation of polyurethane-modified acrylic resin emulsions and their application in coatings are introduced in CN1664032, CN101157749 and U.S. Pat. No. 6,635,706. However, such polyurethane-modified acrylic resin composite emulsions are utilized only in the field of coatings, they are not suitable for preparing ink products, laminating adhesive, gloss varnish for woodware, or the like. The present inventors believe that the polymer products prepared by different methods have different functions and applications. Emulsion polymerization is a heterogeneous polymerization, so that the polymer emulsion is a dispersion of latex particles in water. Solution polymerization is performed in a solution and the product obtained is solvent-based type. In subsequent applications, the polymer solution forms a fine and tight polymer film after volatilization of the solvent and solidification; while the polymer emulsion forms a coat film via the dispersed latex particles penetrating and diffusing with one another and then aggregating to an integral at a temperature higher than the minimum film-forming temperature of the emulsion. The synthetic resins obtained by emulsion polymerization and by solution polymerization respectively have different properties and applications due to their different film-forming mechanisms. So far, however, there is no report regarding research of synthetic polyurethane-modified acrylic resin prepared by solution polymerization.